The present invention relates in general to communication systems, and is particularly directed to a digital communication link pre-establishment control mechanism, that is incorporated into the communication control software employed by the microcontroller of customer premises-installed digital subscriber loop (DSL) terminal equipment, and which is operative to automatically determine the bit rate of high-level data link control (HDLC) digital communication service to which the customer has subscribed.
Digital subscriber loop (DSL)-based communications, such as integrated services digital network (ISDN) services, enable telecommunication service providers to supply multiple types of digital signalling channels from a central office to a network termination interface or DSL terminal equipment, such as, but not limited to an ISDN phone, an X.25 packet device, or an ISDN terminal adapter, to which customer premises-resident data terminal equipment may be coupled.
Since the DSL terminal equipment is customer-purchased and installed, the telephone service provider does not participate in the customer""s choice of the device that is connected to the DSL line. However, in order for a customer to be able to connect and conduct digital data communications through an installed piece of DSL terminal equipment, it is necessary that the DSL terminal equipment""s supervisory communications controller be properly initialized or preconfigured with a prescribed set of DSL communication parameters as defined by the service provider. One of these parameters is the data rate which, in the case of T1 network as a non-limiting example, will be based upon the number of DS0 channels (up to twenty-four 64 kbps channels per T1 link) to which the customer has subscribed.
Now although this and other parameter information of the subscription service are provided by the telephone service provider to the purchaser of the terminal equipment, the user is usually technically unsophisticated and accustomed to doing nothing more than simply performing a xe2x80x98plug-and-playxe2x80x99 exercise. Experience has revealed that a very large majority of DSL customers will burden the equipment supplier and/or the local telephone service provider with requests for technical support in the course of configuring the settings for CPE terminal equipment, irrespective of whether the service provider has correctly supplied each of the parameters of the customer""s terminal equipment.
In accordance with the present invention, the user""s (actual or perceived) inability to properly configure an installed piece of DSL terminal equipment, in particular, setting the proper DSL bit rate, even when provided with correctly assigned operational parameters by the telephone service provider, is successfully remedied by an automated data rate detection mechanism, resident in the control software employed by the microcontroller of customer premises-installed DSL terminal equipment. As will be described, this automated data rate detection mechanism is operative to monitor the bit contents of digital signals conveyed over the DSL link to which the customer""s equipment is connected and, based upon an analysis of those bit contents, automatically determines and sets the bit rate of the customer""s equipment to conform with that of the (HDLC) digital communication service being supplied by the service provider.
For this purpose, during idle mode, the bit contents of a T1 frame of bits sourced from the network DSL device at the central office are examined to identify the number of idle bytes within the frame. Detection of idle bytes is based upon the fact that industry standard HDLC signaling practice is to transmit prescribed xe2x80x98idlexe2x80x99 codes (0111 1110) during the time slots used by a respective CPE DSL device when no data is being transmitted, and an all xe2x80x981xe2x80x99s bit pattern (1111 1111) in each of the other time slots that is unused by that device. Since each idle byte contains two and only two zeros, while all unused DS0 time slots contain only ones, the number of subscribed DS0 increments and therefore the number of 64 kbps sub-bandwidth increments may be readily determined by looking for the first occurrence of an idle byte following one or more all xe2x80x981xe2x80x99s bytes, and then counting the number of zero bits until further unused (all xe2x80x981xe2x80x99s-containing) DS0 channels are encountered. Dividing the total number of zeros counted by the value of two will necessarily represent the number xe2x80x98nxe2x80x99 of assigned DS0 increments. Multiplying this number xe2x80x98nxe2x80x99 by the bit rate per DS0 channel (64 kbps) yields the bit rate needed for error-free data transfer between the DSL network device and the CPE installed DSL equipment.
Because the bit rate detection mechanism of the invention does not depend upon particular skill or knowledge of the user, it is especially useful to accommodate a change in the subscribed-to bit rate. For example, if the customer subscribes to an increased (DS0) channel capacity, as a non-limiting example, the invention will enable the customer premises equipment to automatically reconfigure itself for the new rate. Once the new (e.g., higher) rate has been assigned by the customer service provider, running an initialization routine containing the bit rate determination mechanism of the invention will result in the customer""s DSL device detecting the additional one or more DS0 channels, and adapting itself to the new bit rate.